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Lec 16, Ch.8, pp.312-328: Delay progression, and ramp metering (objectives)

Lec 16, Ch.8, pp.312-328: Delay progression, and ramp metering (objectives). Learn how to estimate delays using the Webster delay model Be familiar with a few methods for timing signals of arterial routes Understand the concept behind ramp metering (through reading and video)

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Lec 16, Ch.8, pp.312-328: Delay progression, and ramp metering (objectives)

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  1. Lec 16, Ch.8, pp.312-328: Delay progression, and ramp metering (objectives) • Learn how to estimate delays using the Webster delay model • Be familiar with a few methods for timing signals of arterial routes • Understand the concept behind ramp metering (through reading and video) • Skip pp. 316-318 actuated signals (CE562)

  2. What we cover in class today… • Steps to estimate delay using the Webster delay model • Signal timing of arterial routes (concept only, CE562 & 662 discuss signal coordination in detail) – see if you can identify these in the field • Freeway ramp metering

  3. Delay estimate using the Webster delay model (Know where you get the values from) Delay is a measure of effectiveness of intersections. The Webster delay model gives average stopped delay at a signalized intersection. where dj = average delay per vehicle on j-th approach during i-th phase. Pay attention to these units! C = cycle length (sec) Vj = adjusted peak volume (i.e., flow rate) on j-th approach (pc/lane/sec) i = proportion of cycle length that is effectively green, Gei/C xj = degree of saturation for the j-th approach, Vj/ isj sj = saturation flow for the j-th approach (pc/lane/sec), hence is isjcapacity P = % correction, ranging from 5% to 15% for normal conditions

  4. Methods for timing signals of arterial routes One-way streets: Usually “Progressive” system

  5. Methods for timing signals of arterial routes (cont) Two-way with preference on one direction

  6. Methods for timing signals of arterial routes (cont) Two-way with equal treatment of both directions: n = number of signals in one simultaneous pattern

  7. Freeway entrance (on) ramp control • Justification: You need to justify the installation of ramp metering because it may increase delays of those who try to enter freeways more than justified. • Ramp metering must result in a reduction of the total expected delay to traffic in the freeway corridor, that includes freeway and local streets. Rate = 4 to 15 veh/min • Criteria: At least one of these must be satisfied. • Recurring congestion exists in the main flow OR a severe accident hazard at the freeway entrance • Signals (meters) are needed to accomplish transportation system management objectives • Signals are needed to solve congestion problems caused by non-recurring congestion  ball games, etc.

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